Conveyor belts are widely used for moving minerals, coal, and a wide variety of manufactured products from one point to another. Heavy duty conveyor belts used in mining operations can extend over distances of several miles and represent a high cost component of an industrial material handling operation. Unfortunately, such conveyor belts are susceptible to damage from the material transported thereon and a rip, slit, cut or tear may develop within the belt. For instance, sharp edges of the material being transported can gouge the surface of the belt and that can result in a rip developing.
After being detected a torn or ripped belt can be repaired. However, the cost of repairing a heavy duty conveyor belt and cleaning up material spilled as a result of the damage can be substantial. In cases where such damage is not detected and repaired promptly, the rip typically propagates along the length of the belt with continued use of the conveyor system which makes the repair even more difficult and costly. It is accordingly desirable to detect damage to the belt as soon as possible after it occurs and to quickly repair the damaged area of the belt. By doing so the extent of the damage to the belt can be minimized and the spillage of material being conveyed can be reduced.
Over the years, a number of systems have been developed for detecting belt damage and for automatically stopping further movement of the belt after the damage occurs. It is well known to employ sensors within conveyor belts as part of a rip detection system. In a typical system, sensors in the form of loops of conductive wire are affixed or embedded in the belt and provide a rip detection utility as part of an overall rip detection system. Rip detection is achieved through the inferential detection of an “open circuit” condition in one or more of the sensor loops in the belt. Typically, an electrical energy source external to the belt is inductively or capacitively coupled to a sensor loop in the belt. A break in the conductive wire loop of the sensor may be detected by a remote transmitter/receiver (exciter/detector). Disposition of a plurality of such sensors at intervals along the conveyor may be effected with each sensor passing within read range of one or more exciter/detectors at various locations. In this manner, the existence of a tear will be promptly detected and repaired with further damage to the belt being minimized.
U.S. Pat. No. 3,742,477 discloses a “figure eight” sensor loop useful within a belt sensor system. U.S. Pat. No. 3,922,661 discloses an electronic control system for conveyor belts which monitors the condition of embedded sensor conductors in the belt and provides a warning indication and/or shutdown of the conveyor when damage occurs to the belt or control circuitry.
U.S. Pat. No. 4,621,727 discloses a reinforced conveyor belt having included therein a conductor for use in a rip monitoring system, said belt comprising: (a) an elastomeric body having an upper carrying surface and a parallel lower pulley engaging surface, each surface extending indefinitely in a direction of travel of the belt; (b) a plurality of reinforcement layers positioned within said elastomeric body; (c) a plurality of envelopes of low coefficient of friction material positioned within said elastomeric body and spaced apart in the direction of travel of the belt, wherein each envelope establishes a void area in said elastomeric body within said envelope; and (d) a shaped conductor positioned within said envelope such that said conductor is free to move within said void area during operation of said reinforced conveyor belt.
U.S. Pat. No. 4,854,446 discloses “figure eight” sensor loops disposed at intervals along a conveyor belt. This reference more specifically reveals an endless conveyor belt having a direction of travel comprising: (a) an elastomeric body having a load carrying surface and a parallel pulley engaging surface; (b) a reinforcement ply disposed within said elastomer body; and (c) a conductor, disposed within said belt in a predetermined pattern forming a closed current path; and wherein said conductor comprises a plurality of strength filaments or strands of a first metal wrapped about a conductive core of a second metal, said strength filaments or strands having a higher fatigue resistance than the conductive core, for increasing the fatigue resistance of the conductive core.
U.S. Pat. No. 6,715,602 discloses a conveyor belt incorporating within it a rip detection sensor comprising a conductor formed in an endless loop, characterized in that: the belt includes at least one transponder secured to the belt in coupled relationship with the conductor; and the transponder transmits information identifying the location of the conductor along the belt.
U.S. Pat. No. 6,352,149 discloses a system in which antennae are embedded in a conveyor belt to couple with an electromagnetic circuit consisting of two detector heads and an electronic package. Coupling occurs only when an antenna passes across the detector heads and can only occur when the loop integrity has not been compromised. U.S. Pat. No. 6,352,149 more specifically reveals a conveyor belt incorporating within it a rip detection sensor comprising a conductor formed in an endless loop arranged in a signal inverting configuration wherein the conductor crosses itself in at least one crossing place, characterized in that: the conductor is formed as microcoil springwire; the conductor crosses itself by crossing through itself such that the microcoil springwire resides substantially in a single plane throughout the sensor including the crossing places; and means for preventing short-circuiting of the conductor at the crossing places.
The performance and reliability of microcoil springwires utilized in conveyor belt rip detection systems, such as the system disclosed by U.S. Pat. No. 6,352,149, can be compromised due to breaks, micro-breaks, or partial breaks therein which are caused by the microcoil springwire being elongated beyond its breaking point during the normal operation of the belt or as a result of belt damage. In other words, the microcoil spring wire can be damaged during normal belt operations as a consequence of ordinary wear and tear or it can be damaged by a high level of strain which is encountered during a high elongation event which causes the belt to stretched beyond the levels encountered during normal operations. In any case, the microcoil sensor wires utilized in the rip detection systems of conveyor belts can are susceptible to damage which is typically the result of being elongated beyond the break point of the microcoil sensor wire. The presence of breaks, micro-breaks, or partial breaks in the microcoil springwire compromises its electrical properties and accordingly adversely affects the performance and reliability of the rip detection system. There is accordingly a need for microcoil springwires that are highly durable, less susceptible to damage, and which can be integrated into conventional conveyor belt rip detection systems. Such microcoil springwires must also be capable of functioning in a manner which does not compromise the functionality or reliability of the rip detection system of the conveyor belt.